The present invention relates to a circuit board testing apparatus and method and in particular, to a wiring test using electrostatic capacity.
In Japanese Patent Application Laid Open No. 4-248477, a printed circuit board testing apparatus using a flying probe is disclosed. Such a testing apparatus is equipped with X- and Y-axis servo sections that drive an X-Y table on which a circuit board to be tested is mounted. A Z-axis servo section drives a probe head. To be more specific, the testing apparatus operates to test a desired pattern for continuity and shorts by moving the X-Y table so that the probe head is positioned on the pad section of the pattern, as well as by driving the Z-axis servo section so that the probe head contacts the pattern. When the pattern has been tested, the Z-axis servo section allows the probe head to leave the pattern, followed by moving the X-Y table so that the probe head is positioned on the pad section of a pattern to be subsequently tested. The foregoing enables circuit boards of any kind to be tested by changing only the position of the pad section. In testing apparatus of this type, however, the following problems are encountered.
To move the probe head from one pad to another, the X-Y table cannot be moved unless the probe head is kept away from a contacted pad. Therefore, supposing that one printed pattern requires several milliseconds of time or so for the Z-axis transfer and that several thousands of tests are conducted for a single circuit board, this means that several tens of seconds or so will be required for the Z-axis transfer of a single circuit board.
Furthermore, allowing the probe head tip to contact the pad section may result in scars on the pad section. Because a finely pitched pad section in particular is small in size, it suffers a greater adverse effect of such scars.
Accordingly, it is an object of the present invention to provide a printed circuit board testing apparatus and method which makes it possible to solve the problems mentioned above and to test wiring quickly without causing damage thereto.
In fulfillment of the foregoing object, a circuit board testing apparatus is provided with a first terminal that is to be coupled in a non-contact manner to either end of test wiring of a printed circuit board to be tested, a means that transfers said first terminal over the surface on which test wiring of said circuit board is to be carried out, while maintaining said non-contact condition, means that supplies a test signal to the other end of said non-contact coupled test wiring, and a means for determining test wiring of a circuit board to be tested for continuity and shorts based on a signal that is detected from said non-contact coupled test wiring.
The foregoing of course eliminates the need to move the first terminal toward and away from the circuit board surface, thus reducing testing time. Furthermore, since the terminal at one end can be determined for continuity and shorts in a non-contact manner, there is no risk of flaws on said terminal.
Further, an insulating sheet is provided between said first terminal and said circuit board to be tested and is preferably made of a material which provides excellent sliding characteristics.
Still further, a circuit board testing apparatus is provided with a first terminal shaped to provide excellent sliding characteristics over said insulating sheet.
The test signal has a rapid change characteristic and the determination means monitors the wiring for continuity based on the maximum current generated between said test wiring and said first terminal after a rapid change has occurred in said test signal. The maximum current is generated almost simultaneously with the occurrence of the rapid change in the signal allowing one to know the continuity condition of the test wiring in an extremely short period of time.
When testing a circuit board has been completed for continuity and short determination, the first terminal is transferred over the surface on which the test wiring is formed while it is kept away at a distance which allows non-contact coupling with said circuit board, and is followed by coupling one end of subsequent test wiring with said first terminal in a non-contact manner. A test signal is supplied to the test wiring that is coupled with said first terminal in a non-contact manner and test wiring of the circuit board is determined for continuity and shorts based on the signal detected at said first terminal.
Terms used in this specification are described below:
The term xe2x80x9ccircuit boardxe2x80x9d refers to a base material on which wiring can be or has been formed, and is not limited in terms of its material, structure, shape, or size. It includes, for example, glass epoxy substrates and film-like substrates as well as packages on which circuit elements such as CPUs are to be mounted. It further includes composite substrates wherein sockets are mounted on a glass epoxy substrate and substrates on which circuit elements are mounted.
The term xe2x80x9cwiringxe2x80x9d refers to an electrical conductor and is not limited in terms of its material, structure, shape, or size. It includes conductive parts of printed patterns, through-holes, and pins formed in circuit boards, as well as conductive parts of electric cords, sockets, connectors, and pins attached to the circuit board.
The terms xe2x80x9cone end of the wiringxe2x80x9d and xe2x80x9cthe other end of the wiringxe2x80x9d refer to the points of the wiring to and from which signals for tests are input and output, there is no limitation in terms of material, structure, shape, or size. Included are the sections that form points of electrical contact with other parts, as found in printed pattern testing ends, connector connecting ends, connecting pins, pads for connecting bonding wires, pads for connecting circuit elements or sockets, insertion portions provided in sockets attached to circuit boards, and the input and output terminals of connectors, and also arbitrary locations in the wiring.
The term xe2x80x9cnon-contact couplingxe2x80x9d refers to the coupling of two or more members in such a way that they can transmit and receive signals to and from one another while remaining insulated from one another. In the present invention, this corresponds to electrostatic coupling that uses electrostatic capacity, but is not so limited.
The term xe2x80x9csignalxe2x80x9d refers to a signal used for testing. This concept includes both voltage and current. Besides AC signals such as sine waves, it includes DC signals, rectangular and triangular signals, and pulse-like signals.
The expression xe2x80x9cbased on the signal detected from the non-contact coupled test wirexe2x80x9d means that something is based on said detection signal itself or a physical quantity corresponding or relating to said signal. Thus, it includes not only a voltage signal but also, for example, a current corresponding or relating to said voltage, as well as integral and differential values thereof.
The term xe2x80x9cdetection of continuity of the wiringxe2x80x9d includes the detection of an open or short circuit of the wiring, and the detection of the resistance value of the wiring such as the detection of a half-open-circuit.
The term xe2x80x9csignal with a rapid changexe2x80x9d refers to a signal with a large amount of variation in voltage or current per unit time, and includes, for example, DC signals with a step-like rising or falling edge, triangular and rectangular signals, and pulse-like signals.